Club drug use has increased dramatically in the United States over the last decade. These drugs, including MDMA, Ketamine, GHB, 2C-B, and Methamphetamine, have diffused from subcultures, particularly the rave scene, and are now used in multiple scenes and settings. Despite these recent trends, there remains little published research on the use of these drugs in America, particularly on initiation by young people. Though club drug research agendas have been more firmly established in other Western nations, much work remains in the United States. We do not yet have an understanding of the patterns of club drug use by American youth, including who, how, when, and where young people use these drugs. Since club drug use is a recent phenomenon, it is important to gain an understanding of how youth are being initiated, so as to understand the process of diffusion of these drugs. Research on mobile suburban (bridge and tunnel) youth in Manhattan can provide foundational understandings of club drug use among youth. These youth are a population involved in multiple social contexts, urban social scenes as well as their everyday suburban social existence. Thus, engaged in multiple social worlds, these youth offer information on the patterns of club drug use in varied social settings. Also, youth who travel from the suburbs to Manhattan are a bridge population; that is, they are potential routes of infectious disease transmission from urban youth to youth in surrounding suburbs and vice versa. Yet, aside from the traditional manner in which bridge populations are thought of, and perhaps more importantly, bridge and tunnel youth are vehicles for the diffusion of health beliefs, social norms, and practices pertaining to club drug use between populations who may not otherwise directly interact. Aside from the growing concern over the toxicity and potential for overdose with these drugs, the use of these drugs enables risky behaviors. Certain routes of administration place youth at risk for health problems, such as HIV and Hepatitis. Furthermore, there is little understanding of the potential sexual risk behaviors attributable to the use of these substances by young people. Determining the pathways to club drug initiation and transitions to later stages of use and abuse is, therefore, of utmost importance. [unreadable] [unreadable]